Utah's Pandemic Earthquake of March 2020

Continuing on through my pile of photos I come across the start of the lockdown in March of 2020 and I am reminded that at the very start of the lockdown, Utah was hit with the largest earthquake it has seen in recent memory and the largest earthquake I personally have ever been a part of. 

On the morning of March 18th, 2020 at 7:09 am local (MST) time, western Salt Lake County was hit with a 5.7 magnitude earthquake. At the time we lived in the valley to the west, not 13 miles from the epicenter of the earthquake. The epicenter is the spot on the surface directly above where the fault moved (known as the focus). Earthquakes occur due to energy that is released after a slip occurs along a fault. This energy produces shaking in the ground, both up and down, side to side, and back and forth. This motion of the ground is what we feel on the surface. 

Upon the start of the earthquake we were getting ready for our day. The wife was getting ready for work, the child, having off of school that week for spring break, was playing in her room, and I was still in bed. Upon the start of shaking I jumped out of bed and grabbed her from her room into the doorframe of my bedroom since our bedrooms were directly across the hall from each other. 

The doorframe is one of the safest locations in a home during an earthquake because structurally it is one of the strongest spots. Lights, parts of ceiling, pictures, and stuff on shelves are less likely to fall on you in a door frame. Walls are also less likely to collapse there. Under a desk or table is also another safe location for the same reason, the structure will provide protection from falling objects. Running outside is actually a terrible idea because the initial shaking of an earthquake only lasts a couple of minutes at most, and in that time you won't get very far and around the outside of a building is the most dangerous place to be since things like bricks can fall off a building and glass can break from windows. So, stay put in a safe location, if possible.   

Above is the initial shake map from the earthquake from the USGS. Earthquake.usgs.gov is my favorite website for quickly identifying earthquakes and their sizes and locations. The website is updated within about 5 minutes of an earthquake. This is also helpful during the numerous aftershocks we felt to wonder if they were an actual aftershock or just a passing truck. The shake map tells you the location and the size of the earthquake, as well as how far away it was likely felt. This information will get refined over the coming hours and days as more information is obtained.

One of the things about an earthquake that I never realized is that I was constantly feeling aftershocks for months afterwards, regardless if we actually had them or not. Having never been in an earthquake, I thought it would be super cool as a geologist to be part of one. I was wrong. It was terrifying. And still is, because there is no warning and no way to really get mentally prepared except to have everything you need in the event that one happens and your home or place of work to be structurally prepared. 

Within a few hours the area was inundated with aftershocks including four of a magnitude 4.0 or greater. The above map represents the shake map of the 4.6 aftershock that hit in the afternoon of March 18th. 

Above is the most up to date shake map of the main, 5.7 Magnitude earthquake. This is what is called a Modified Mercalli Map, which uses people's real life experiences to help shape the impact of the event. If something fell of a shelf in your house you would have felt a different different level of intensity than if your entire house fell down. Each of those dots represent points of data where someone contributed to the map. If you are a part of an earthquake, this is a great way for everyday citizens to participate in citizen science at USGS's Did You Feel It. 

As identified by the University of Utah Seismographic Station, there were over 2,500 earthquakes that took place in the same area from March 18th through the following year. 

UUSS's seismic graph from earthquakes.utah.gov.

Of all those 2,500+ earthquakes, all but one was identified as an aftershock, the one being the main event earthquake. An aftershock is an earthquake along the same fault line that occurs after the main earthquake and is always lower in intensity. If for some reason we had an earthquake that was a 6.0 after the 5.7, the 6.0 would not be considered an aftershock. At that point the 5.7 would be renamed a foreshock (taking place before the main earthquake) and the 6.0 would become the main earthquake. So in actuality, aftershocks are only identifiable as such as long as they are smaller than the main earthquake and to understand the entire picture of an earthquake, some time has to progress until we see all of the impacted fault movement and earthquakes.  

The Basin and Range Province. Image courtesy of Miracosta.edu.

Geologically speaking, Utah is located along the eastern edge of what is called the Basin and Range Province. This is an area that is actively undergoing extension. Meaning the the plate is essentially being stretched apart here. The result of which is what we see, a series of parallel, north-south running mountain ranges with valleys in between. Intermixed with all of this is a series of volcanic eruptions occurring all over the region due to the thinning crust. I had covered a bunch of Utah's volcanic legacy in a previous post HERE.

Extensional activity in the Basin and Range Province. Image courtesy of Miracosta.edu.

The types of faults most commonly associated with this type of extensional activity is known as a Normal Fault. 

A Normal Fault is where the overriding block (the hanging wall or head wall) moves downward in relation to the under-riding block (the footwall). 

Location of the Wasatch Fault in Salt Lake City.

Along the eastern edge of the Salt Lake Valley is the Wasatch Fault, the largest fault in the region, and also a Normal Fault. Generally it is considered a "fault zone" because of all of the offshoots and short segments of the fault, especially since scientists are not 100% sure about where exactly the fault is located in all locations. 

Wasatch Fault Scarp in Salt Lake City

Where the fault does hit the surface in a fairly well identified area is in the eastern edge of Salt Lake City, where a fault scarp can plainly be seen. A fault scarp is the cliff or surface disruption along the surface rupture of the fault where the two blocks can easily be identified, as in the picture above, because the one block juts up compared to the other block. But a fault isn't likely to cause an earthquake just where it surfaces. The fault also extends many miles below ground. And as can be seen in the diagram above and below, the Wasatch Fault curves towards the west, below the Salt Lake Valley.

A great graphical representation of the Wasatch Fault below ground from earthquakes.utah.gov.

And that is where the earthquake of March 18th occurred on. The movement occurred on the Wasatch Fault, but it occurred 6 miles (10 km)  below the surface. This is the reason why although the fault lies along the eastern part of the Salt Lake Valley on the surface, the earthquake occurred almost on the western edge of the valley on the same fault. 

Right now it is estimated that an earthquake of a 7.0 to a 7.6 will occur sometime in the future along the Wasatch Fault Zone. This is based on historical estimates of the previous earthquakes along the fault and size estimates based on the size of the fault. Earthquakes are only able to generate energy based on the size of the fault. The larger the fault, the larger the potential earthquake. So, based on the size of the Wasatch Fault, a 7.6 would be the maximum size that an earthquake could be. However, that would be detrimental to the region because many buildings and other infrastructure are not built to withstand an earthquake of that magnitude.

The odds of a 7.0 earthquake occurring within our lifetimes is generally on the low side, though. So, although there is no reason to constantly live in fear, there is reason to build our community with earthquake resiliency in mind. Especially since our buildings will hopefully far outlast us. 

Geological Destination - Monument Valley Tribal Park

Back in November of 2019, while driving back from Arizona to the wife to do one of her Iron Man races, we drove through one of the Navajo Nation Tribal Parks, Monument Valley Tribal Park. As a runner, my wife wanted to get a shot of her running up the Forest Gump hill, while as a geologist, I just like looking at the pretty rocks.

Slightly downhill from us but essentially the same view in Forest Gump

As can be seen in the image, this is easily an icon geological location. The rock units within Monument Valley are essentially the same as the rock units within the nearby Canyon de Chelly National Monument, however the landscape is a bit different. Instead of the rocks being isolated within a canyon system like at the park, they are now elevated above the surrounding landscape. This is likely an effect of the Colorado Plateau, where this region had been slightly elevated compared to the areas further down south. A breakdown of the rock units within each of the mesas seen in the background is as follows:

Monument Valley geology. Image courtesy of the UGS.

The Shinarump, is part of the Chinle Formation, a Late Triassic (~225 million years old) yellow-grey river-deposited sandstone and conglomerate. 

Below the Shinarump is the Moenkopi formation. The Moenkopi Formation is an Early to Middle Triassic formation (~245 million years old) that is is predominantly made up of the reddish-brown shale. The Moenkopi was deposited within an intertidal environment, with alternating sea levels producing thinly bedded layers of mud (shale) and sand (sandstone). 

Below the Shinarump is the De Chelly Sandstone. The De Chelly Sandstone is a Permian age (~200 million years old) aeolian sandstone. Aeolian means that it is formed by blowing wind, in particular sand dunes, or a desert environment. When sand dunes are frozen in time, such as when they become rocks, and eroded you can see features termed cross-bedding. These rock preserve an ancient sand sea desert, known as an erg, that used to be located here. Sandstones are also frequently extremely hard rocks that are resistant to weathering. When they weather, they fracture into regular joints. Those are the vertical line patterns of the rocks as seen in the image above. It is also what produces the shear-walled rock mesas as we know them today. 

Below the De Chelly Sandstone, is the more erodible Organ Rock Shale. You can tell it erodes much more easily by the smooth slope that forms from the edge of the overlying sandstone. If the sandstone wasn't there to protect the shale, the shale would have eroded long ago. The Organ Rock Shale is another Permian formation (~270 million years old), that mainly comprised of mudstone (shale) and siltstones. They were deposited by streams within a tidal flat environment. The Organ Rock Shale then underlies much of the surrounding landscape which is then covered over with much, much younger (Quaternary) sediment (known as alluvium) transported in by winds and water from these and other surrounding rock formation.

Geological Destination - Four Corners Monument

Being located at the junction of four states, Four Corners Monument might just as well be considered a political park. However, geology is everywhere and therefore this is a perfect example of a geological park as well. The Four Corners Monument is a Navajo Tribal Park that designates the boundaries between the states of Utah, Arizona, Colorado, and New Mexico. It also designates the boundaries between the Navajo Nation and the Ute Mountain Ute Tribe Reservation. We visited the park on my birthday back in March of 2019. 

Me, laying across all four states at the monument. 

It has been said, by many people, that this point does not actually represent the point of intersection of the four states. These people are wrong. As noted by NOAA:

"... the Four Corners monument was established at the point he [surveyor Chandler Robbins] determined, to the very best of his ability and using the available technology, to be the prescribed location of 109 degrees 03 minutes West longitude and 37 degrees North latitude."

This precise location, however may be off by ~1,800 feet to the west of the monument. However, since this point was surveyed as the junction of the four states, and approved by the governments of the four states as well as the federal government, it IS the location of the junction, regardless of what the original intention of the surveyor may, or may not, have been.

It should also be noted that acclaimed geological landmark, nearby Ship Rock, was used as one of the marker locations for the designation of the Four Corners Monument. My next post will be on Ship Rock.

A closer look at the geodetic survey marker, designating the actual Four Corners point.

The Four Corners Monument sits within the Colorado Plateau. An area that is being forced upwards by the subducted Farallon Plate. 

Location of the Colorado Plateau. Image courtesy of Woodward, 1973.

Starting ~100 million years ago, along the west coast of North America was a subduction zone. This is where one plate goes beneath another plate. In this instance the Farallon Plate subducted, or went beneath, the North American Plate.

Graphic of the Farallon Subduction. Image courtesy of the NPS.

Over time the majority of the Farallon Plate was completely subducted, including the mid-ocean ridge (aka spreading center), leaving behind a new type of plate boundary along the coast of California. Instead of a subduction zone, there now was left a transform plate boundary, where one plate slides passed another one. This plate boundary is better known as the San Andreas Fault. Remnants of the Farallon Subduction Zone still exist along the coasts of northern California, Oregon, and Washington. 

Over the past ~10 million years, the subducted Farallon Plate was still a very hot plate, and therefore wanted to rise up underneath the North American Plate. Because of this, the Farallon Plate started to push upwards on North America, creating a region of the continent that is rising vertically upwards compared to the surrounding regions. This is the Colorado Plateau.

The geological features of the Colorado Plateau surrounding the Four Corners Monument. Image courtesy of Woodward, 1973.

The Colorado Plateau is made up of many of the world's most beautiful landscapes because of these geological forces playing around in the region. Looking specifically at the Four Corners region, anyone who has been to the Four Corners Monument will also notice that this area is a relatively flat, mountainless plain. This region is known as the Four Corners Platform. The platform is a relatively flat region that sits as an intermediary between adjacent basins and uplifts. In an area surrounded by mountains and canyons (and several anticlines (A-shaped bends in the rocks)) this region just happens to be in the middle of it all forming a flat surface. 

Geological Map of the Four Corners Monument. Image courtesy of NGMDB.

Looking at the rock units that cover the Four Corners Monument, they are represented on the map above by the symbols Jmw and Jmb, These are both members of the Upper Jurassic Age (~585 million years old) Morrison Formation. The Brushy Basin Member (Jmb), which covers the actual monument, is an interbedded green, purple, and grey mudstone and siltstone with grey and tan sandstone and conglomeratic sandstones. Known for its dinosaur fossils, the Brushy Basin Member was deposited from prehistoric rivers (fluvial) and lakes (lacustrine). The underlying Westwater Canyon Member (Jmw), is a yellowish-grey sandstone containing conglomeratic lenses and dark-reddish-brown siltstone. The Westwater Canyon Member is also a fluvial (river) deposited unit.

References

https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.544.8012&rep=rep1&type=pdf

https://www.ngs.noaa.gov/INFO/fourcorners.shtml

https://bluffutah.org/four-corners-monument

https://ngmdb.usgs.gov/mapview/?center=-108.996,36.967&zoom=10

https://ngmdb.usgs.gov/Prodesc/proddesc_4550.htm

https://www.sciencedirect.com/science/article/abs/pii/0037073889900705

https://sed.utah.edu/Morrison.htm

Geological Destination - Dead Horse Point State Park

 Just outside of Moab, UT, lies a State Park with fantastic overlooks and great geology. We stopped at Dead Horse Point State Park on our way to Canyonlands National Park back in March of 2019. The two parks are pretty close to each other and we had heard good things about the state park. And we were not disappointed.

The name of Dead Horse Point comes from a legend where cowboys would fence off wild mustang horses along the overlook, taking what horses they wanted and leaving the horses they didn't penned up to die of thirst. But despite the grizzly imagery, this is a beautiful location.

Looking off towards the southeast from the overlook is the Colorado River far below. Between us and the river lies 100 million years of geological history. From top (youngest) to bottom (oldest) the rock units go like this:

Entrada Formation: Jurassic (150 million years old) - This is a sandstone formed from a coastal dune environment. These are what the arches at Arches National Park are found in.

Navajo Sandstone: Jurassic (175 million years old) - Wind deposited, prehistoric "petrified" sand dunes from an ancient erg (sand sea), colored a light tan or white color. The units also preserve phenomenal cross bedding features from the sand dunes. These rocks form the majority of the rock formations in Zion National Park.

Kayenta Formation: Late Triassic (180 million years old) - A series of sandstones, shales, and limestones from a meandering river environment that frequently preserves dinosaur tracks. This formation is very well observed in the nearby Canyonlands National Park.

Wingate Sandstone: Triassic (200 million years old) - Like the Navajo, another wind deposited preserved series of sand dunes, however usually with more of a red tint to the rocks (rust). 

Chinle Formation: Triassic (210 million years old) - A stream deposited series of mudstone, sandstone, and conglomerates. Well known for containing uranium deposits, petrified wood, and fossils. You can see some of the ancient uranium mines in nearby Capitol Reef National Park.

Moenkopi Formation: Early Triassic (230 million years old) - A tidal flat deposited series of brown to red mudstones. The rocks will often feature ripple marks and raindrop imprints. You can see this formation especially well along the western entrance to Capitol Reef National Park.

Cutler Formation: Permian (250 million years old) - Comprised of sandstone and conglomerate, this formation was deposited along a coastal-marine beach with off-shore sands and non-marine alluvial floodplain deposits intermixed. The most notable feature of the Cutler is the White Rim Sandstone.

Honaker Trail Formation: Pennsylvanian to Permian (286-320) - Down at the level of the river lies this shallow sea deposit comprised of dark grey limestones with fossils. 

Off in the distance to the east of the Point are some Solar Evaporation Ponds. These are rather striking in the sea of reds and browns that I'm glad they had an interpretive sign to help understand what you are looking at. 

Description of the salt deposits being mined.

This entire area is part of the Colorado Plateau and is the reason that we have the Colorado River formed within the canyons as you can see here. Over 10 million years ago the Colorado River was flowing along a gently sloped floodplain, being allowed to meander as it needed to. Then the area was forced upwards. This occurred when the Farallon Plate, a large plate that was subducted below North America off the western coast of the the US, began to push upwards on the region. As the region was forced upward, the rivers that were formally allowed to meander naturally, started to erode downwards into the underlying bedrock. This downward erosion locked the rivers in place, creating a feature known as an entrenched meander. Besides just here, you can see this feature all over the Colorado Plateau including at the Grand Canyon National Park, Natural Bridges National Monument, and Goosenecks State Park.

Geological Destination - The Bingham Canyon Mine

Identified as the largest open pit mine in the world, the Bingham Canyon Mine, also known as the Kennecott Copper Mine, is a local attraction here in Salt Lake City. The mine sits within the Oquirrh Mountains, on the opposite side from where I live. I had the frequent hopes of grabbing a good photo of the mine taking off from the Salt Lake airport and that time finally arrived when flying down to Las Vegas a couple of years ago. 

View of the Bingham Canyon Mine facing west

In the photo above you can see the mine nestled within the Oquirrh Mountains. The mountains in the background are the Stansbury Mountains with the Tooele Valley (where I live) located in between. 

View of the Oquirrh Mountains facing the western side of the mountains

Above is a view of the Oquirrh Mountains from the western side of the mountains (facing east). The Bingham Canyon Mine is located on the other side of the mountains towards the right (southern) edge of the picture. 

Another shot of the pit a little further along in the flight path.

Per the Utah Geological Survey, the Bingham Canyon Mine:

"...  is one of the largest and most efficient mines in the world. It has produced more copper than any other district in the U.S., accounting for over 16% of total U.S. copper production. In addition to copper, the mine produces gold, molybdenum, and silver. KUC’s combined annual value of these metals peaked in 2011 at $2.9 billion."

Currently the Bingham Copper Mine is the 2nd most active copper producing mine in the US and one of the top gold producers in the US as well. 

Geology

The rocks within the Oquirrh Mountains were deposited a long time ago during the Paleozoic (250 to 540 million years ago). Much of these rocks were deposited in marine environments as Utah represented the edge of the North American continent. Eventually the land started to be raised up and dried off and then around 100 million years ago the Farallon Plate started to subduct beneath the North American Plate.

Diagram of the Farallon Plate subduction zone along the western United States. Image courtesy of the NPS. 

The pressure of the Farallon Plate pushing on the North American Plate did two things. First, it compressed the North American Plate, creating a "wrinkle" in the surface producing mountains along the western part of the US. Second, as the Farallon Plate was subducting, it then started to melt. That melted rock eventually rose up and created a line of volcanoes. Around 30 to 40 million years ago, that line of volcanoes was located within Utah. Magma was slowly injected into the Oquirrh Mountains, predominantly into the 300 to 350 million years old rock formation known as the Oquirrh Group. These rocks, laid down in the Carboniferous (i.e. the Pennsylvanian and the Mississippian), are composed mostly of quartzites and limestone beds. This magma body slowly cooled to form what is known as the Bingham Stock, an igneous body identified as a monzonite porphyry. In addition to the magma body itself, is that the hot magma produces a lot of hydrothermal fluids within proximity of the magma body. These hydrothermal fluids move the heavy metals (such as gold, copper, silver, etc.) from within the magma and redeposit them within the surrounding landscape. 

Model for the magma-hydrothermal mineral deposits. From Groves and Santosh, 2015.

Cross Section of the Bingham Canyon Mine from Kennecott, 1991. Image courtesy of the Society of Economic Geologists. 

Stratigraphic column of the Bingham Pit Mine from Kennecott, 1991. Image courtesy of the Society of Economic Geologists.

So what you are left with is an isolated region that has a high concentration of metallic ore deposits. Many of the more prolific ore deposits across the globe have formed in a similar way (hydrothermal fluids surrounding a magma body) and therefore understanding how the Bingham Canyon mine formed helps us to understand where other ore deposits originated from.  

Geological Destination - Red Cliffs Recreation Area Utah

 

One the great things about Utah is that even when not going to the National Parks, there's literally countless little geological oases that one can find themselves in. One of my favorites is a little campsite/park called the Red Cliffs Recreation Area just outside of St. George, Utah. The park straddles the line between two geological formations, the Kayenta Formation and the Navajo Sandstone, with the boundary between the two running right through the middle of the campground.

Starting within the campground, the Silver Reef Trail almost immediately takes you to one of the paleontological highpoints of the area, the Dinosaur Track Site! These dinosaur tracks are located in the uppermost reaches of the Kayenta Formation. The Kayenta Formation is an Early Jurassic (~190 million years old) mix of reddish-brown sandstones, siltstones, and conglomerates that interbed with each other. These were deposited within a meandering river environment and one of the notable features within the deposits are … dinosaur tracks. 

The lighting on these at the time wasn't fantastic but you can still make them out. I also tried to adjust the contrast and lighting on the picture to emphasize them. Dinosaur tracks are a type of trace fossil. Trace fossils, which I go over HERE, are evidences of behavior of animals without the actual animals being preserved; things like worm burrows or fossilized poop or footprints. Trace fossils are also named like regular fossils but instead of being a genus and species, they are named with an ichnogenus and an ichnospecies (ichno meaning trace). The dinosaur tracks found within this park are identified as Grallator and Eubrontes. It should be noted that the makers of any trace fossils is often up to conjecture. Very rarely do scientists find the animal associated with the trace but often it can be narrowed down by the size and build of the animals around at the time compared to the trace morphology. 

A great place to learn about dinosaur tracks is the nearby St. George Dinosaur Discovery site, which has tons of footprints with many of them preserved in place (in situ) and the building is literally built right on top of them. Of the tracks found at Red Cliffs, Grallator is a 4- to 8-inch-long, three-toed print, that probably belonged to a slender, meat-eating dinosaur such as the 10-foot-long Megapnosaurus. Eubrontes (seen in the center of the picture above) is a larger 13- to 18-inch-long, three-toed print, which is thought to be made by a large meat-eating dinosaur such as the crested Dilophosaurus (think the original Jurassic Park but much, much bigger). 

Above the Kayenta Formation is the Navajo Sandstone creating a amphitheater around the campground. Here is a view over the campgrounds with the Navajo Sandstone in the background. The Kayenta Formation is forming the rocks on the very edge of the left side of the image.

The Navajo Sandstone is a rather famous sandstone, being found in many of the national parks in southern Utah creating fantastic geological outcrops, such as those seen here. The Navajo Sandstone is a very thick (~1000 feet) eolian sandstone from an ancient sand sea known as an erg that formed during the Early Jurassic (just slightly younger then the Kayenta Formation at ~180 million years old). This sand sea was larger than the present day Sahara Desert. 

The Navajo is very well known because of the desert features that are so well preserved in it. The most notable is the cross bedding, which is seen in the pictures above and below. Cross-bedding is a depositional feature of sand that forms during the creation of sand dunes. When wind blows sand, the sand bounces along the ground rolling up the side of a dune (the windward side of the dune). Eventually, it reaches the crest of the dune, and falls over the crest of the dune (the slipface or leeward side of the dune). On the slipface, the grains of sand all form into little parallel rows that curve down at the base. These curved lines are what we see when we are looking at cross beds. 

A cross-bedding diagram. Image courtesy of Teach the Earth.

The different sets of curved lines represent different generations of sand dunes that passed through this area. As winds change, frequently with different seasons, the sand dune migrate in different directions along with the wind. These changing sand dune migrations cause the erosion of previous sand dunes, however the bases of some of the sand dunes may be left behind, which is what is then preserved into rock. Then future sand dunes travel over the old dunes, creating new cross beds. 

These sand grains are cemented with other minerals, often calcite or silica (quartz), creating the rock known as sandstone. Because of the nature of these rocks, the cement will often not fill all, or even most, or the pore spaces, creating a very porous rock. This is one of the reasons that sandstone is a popular water or oil/gas repository known as an aquifer. 

The Navajo Sandstone is also known for these pockmark features along it's surface. This is a type of weathering known as honeycomb weathering. Honeycomb weather is produced as water wicks into the porous rock and dissolves the calcite cement holding the grains together. Eventually the dissolution of the cement allows for the grains to be washed away with future rain events. 

One of the cool features of southern Utah is the ability to hike these gorgeous rock units that have remained mostly intact due to the low amounts of precipitation that the area gets. This low amount of precipitation also produces such gorgeous features such as these slot canyons which are a small hike towards the north of the campgrounds called the Red Cliffs hiking trail. The hike continues up the canyon, however it gets a bit harder from here as evidenced by the hand and footholds carved into the rock on the right and the rope used to get up to the top of this little waterfall.

But as the hike continues it is a gorgeous way to soak in the geology. And generally I have noticed that the crowds are fairly small, especially due to the small size of the campgrounds. Sandstone has a tendency to fracture along naturally occurring joints in the rocks. The joints are then further widened by streams flowing through the area creating the slot canyons as they are seen today.

A little bit of a ways to the south of the Red Cliffs Recreation Area is the Quail Creek Reservoir, which is a great place to spend the afternoon. They allow boating and swimming, but what I want to focus on is this great anticline across the water. We are looking towards the northeast but the anticline cuts right through the middle of the reservoir basically towards where I am standing. These are Triassic age rocks of the Moenkopi Formation and the Chinle Formation, which are older than the rocks found just to the north in Red Cliff Recreation Area and would be located below those rocks. 

Geology of the National Parks in Pictures - Capitol Reef National Park

My next post about the Geology of the National Parks Through Pictures is from a park that we had visited almost on a yearly basis for the last few years and is the park I had easily been to the most.  

You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

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Capitol Reef National Park

My first visit to Capitol Reef was back in 2010 for a geology field trip, for which I had made a geological tour website that is still a fantastic geological resource over at the U of U geology page. A few years after that I had found out that you could pick apples within the park and we planned our family visit for when we could pick the apples. Since then we had made an almost yearly journey down to Capitol Reef in mid fall for the apple picking. 

Despite all these years of going to the park, I only just grabbed an entrance sign shot the last time we went in 2020. 

The most characteristic features of Capitol Reef is the way that the rocks have been folded across the park. With an axis running nearly 100 miles north to south, is a feature called the Waterpocket Fold. There are several different types of folds when we look at rocks. When rocks are folded in a "U" shape, this is called an syncline. When rocks are folded the opposite way, essentially an "A" shape, this is called an anticline. However, when you have a stair-step fold, where one side of the fold is generally horizonal, then its comes down to another horizonal layer, you have what is called a monocline, and that is what the Waterpocket Fold is. You can essentially see this fold in the way that the rocks dip towards the east through much of the park, such as in the image above looking towards the south.

Cross section of the Waterpocket Fold by Ron Blakey. Image courtesy of the NPS. 

Folded approximately 50 to 70 million years ago, the rocks within the park mainly range in age from the Early Permian age White Rim Sandstone (~280 million years old) to the Late Jurassic Age Morrison Formation (~150 million years old). Because of the Waterpocket Fold, the older rocks are easier to see in the western portion of the park and the younger rocks are more exposed in the eastern portion of the park. 

Along the western part of the park is the Goosenecks Overlook, where you can look down into the oldest rocks at the park. The canyon was created by the Sulphur Creek cutting down into the rock units as the rocks were being uplifted. At the base of the canyon can be found the Early Permian White Sandstone. The White Rim is a ~280 million year old coastal sand dune deposit that had been bleached white by hydrocarbons flowing through the rock picking up the iron oxide within the sandstone. On top of the White Rim within the canyon here, and taking up most of the middle of it, is the Early Permian Kaibab Limestone, a ~270 million year old shallow marine shelf deposit that preserves the ancient Kaibab Sea that once flooded most of Utah. 

On top of the Kaibab Limestone is the Lower Triassic age Moenkopi Formation (~245 million years old). The Moenkopi Formation is predominantly made up of the reddish-brown shale that is found throughout the western part of the park. This was deposited within an intertidal environment, with alternating sea levels producing thinly bedded layers of mud (shale) and sand (sandstone). 

Due to the low water levels within the Moenkopi, it preserves many shoreline features such as ripple marks and... 

...animal swimming traces. Here is where a small reptile was swimming along in fairly shallow water and its claws scraped the mud at the bottom. These features can be seen within the gully, just on the south side of the road near the Goosenecks  Overlook. 

On top of the Moenkopi is the Late Triassic Chinle Formation (~200 million years old). The Chinle Formation has a wide variety of rocks types including limestones, shales, sandstones, and conglomerates. Over the course that the Chinle was deposited the environment began shifting from a wetter environment dominated by streams, lakes, wetlands, and deltas, to a drier environment dominated by desert sand dunes. One of the most notable features of the Chinle is the presence of uranium, specifically within the yellow-grey river-deposited sandstone of the Shinarump Member of the Chinle Formation. 

These uranium deposits were often mined in the early 1900's for medicinal uses and the 1950's for its nuclear properties. Eventually, the amount of uranium within the mines wasn't worth the cost of extracting it and the mines were abandoned. 

On top of the Chinle Formation is the Wingate Sandstone. Like I mentioned, the primary reason that we headed to Capitol Reef was for the apple picking in the fall. The orchards are located mostly around the "town" of Fruita within the park. This is where the campground and the Visitor's Center are located. They can also be found extending east to west along the main highway, and the Fremont River, that cuts across the park. But from these you can get some gorgeous shots with the red rocks in the background. The rocks in the background are the Early Jurassic age Wingate Sandstone. The Wingate is a eolian sandstone, meaning that these rocks formed as part a desert ~200 million years ago.

Here is another orchard with the Wingate Sandstone in the background. The Wingate is characterized by those shear vertical cliffs and the red tint to the rock caused by the oxidation of iron coating the sand grains (rust). 

One of the notable geologic features within the Wingate is Cassidy Arch, seen here just above the dead tree in the foreground. 

Here is Cassidy Arch from the top, looking down into the arch. 

On top of the Wingate is the Early Jurassic age Kayenta Formation (~190 million years old). The Kayenta is a mix of reddish-brown sandstones, siltstones, and conglomerates that interbed with each other. The Castle seen here on the left side of the photo from the Visitor's Center, is the vertically jointed Wingate Sandstone, while the Kayenta Formation is more horizontally jointed directly above it to the right.

Like the Navajo Sandstone above it, the sandstone layers within the Kayenta Formation are notable by the eolian formed cross beds, which are angular deposits created as sand dunes move across the desert. Wind blows the sand up one side of the dune, up over the crest of the dune, and then the sand falls down the slipface. The crossbeds are then the preserved record of the slipface side of the dunes locked into place by cement, often calcite or silica.

The Kayenta Formation also contains the Hickman Bridge, a natural bridge carved out of one of the sandstone layers within the formation by the stream flowing beneath it through the softer layers below. 

View from underneath the bridge, hoping to get a good angle emphasizing the "bridge aspect of it.

View from the western side of the bridge. 

Looking west off the Cohab Canyon Overlook  you can see the dip of the beds towards the east as well as most of the rock units we talked about.

Turning around, here is the view to the east from the Cohab Canyon Overlook. On top of the Kayenta Formation is the Early Jurassic Navajo Sandstone (~180 million years old). The Navajo is a very thick (~1000 feet) eolian sandstone from an ancient sand sea known as an erg. The Navajo is notable by its whiter appearance than the reddish Wingate Sandstone and erodes more rounded features, unlike the Wingate which has more vertical jointing. The Navajo also has abundant cross beds throughout the formation. 

The Navajo also has a type of weathering called honeycomb weathering, where these pockmarked patterns occur along the surface of the rock. This is produced as water wicks into the porous rock and dissolves the calcite cement holding the grains together. 

Although the last major rock unit within the park, there are several rock units located above the Navajo Sandstone within the eastern parts of the main highway. These include rocks of the Jurassic age San Rafael Group and the Morrison Formation. 

Looking west from the Hickman Bridge overlook.

References

https://sed.utah.edu/CapReef.htm

https://www.nps.gov/care/learn/nature/geology.htm